Use of scanning electron microscopy to confirm the identity of tropical rat mite (Ornithonyssus bacoti): the cause of rat mite dermatitis.

Cutaneous lesions in human patient due to the bite of rat mite Ornithonyssus bacoti are frequently misdiagnosed as allergies, fungal infection, or bacterial infection. Bite lesions in the personnel working in a Laboratory Animal facility which was infested with O. bacoti is reported here along with its therapeutic management. Diagnosis of the parasites obtained from the clothing of the personnel and later from the infested mice colony was based on preliminary light microscopy and confirmed by scanning electron microscopy. The mean length and breadth of adult female mite were 1.13 mm × 0.63 mm. The body is hairy, unsegmented and has four pairs of legs. The gnathostoma has long pointed chelicerae and pedipalp. The dorsal surface has one dorsal shield, and the ventral surface has three shields- sternal, genital and anal shield. Treatment of dermatitis involved antihistaminic drugs for a period of 3-5 days. The skin lesion, characterized by papular erythema, tends to disappear within a period of 4-5 days of antihistaminic treatment. In untreated cases, the lesions disappeared within 7-10 days. Tropical rat mite O. bacoti Hirst, 1931 was identified to be the cause of infestation in the laboratory mice colony of Pasteur Institute of India, Coonoor, Tamil Nadu, predisposing the animal handlers to be temporary host.